The present invention relates to an apparatus and method for the processing of refuse mixtures including plastic waste, in particular mixtures including a high concentration of plastics waste and/or mixtures of waste packages originating from different collection systems, e.g. from household refuse and industrial refuse, predominantly including plastics in the form of sheeting, hollow bodies, beakers and composite materials, including plastics that may have been contaminated by mineral heavy media such as sands or metal waste.
Certain processes which include wet process operations are known for the reprocessing of these manifold waste mixtures on a technical scale. They are targeted at the recovery of pure-grade plastics as secondary raw materials. The objective of these known methods is to arrive, after several process operations, at a concentration of the plastic waste fractions to be recovered to be followed by a separation of the same by their density.
WO-91/04100 describes a method and an apparatus for the separation of plastic waste by its density via sink-float separation where the substances to be separated are fed at one end into a tank and the floats are withdrawn at the other end of the tank. Drawbacks of this known method are the complicated design of the separating device and the unsatisfactory precision of cut due to the turbulence caused by a belt conveyor running in the separating liquid.
The apparatus disclosed in DE-A-42 08 104 yields a significant improvement to the previously described method. In this case, the suspension, which is made up of the solids to be separated and a separating liquid, is fed centrally into a rotating centrifuge and the solids to be separated are discharged at the two centrifuge ends, substantially separated from the separating liquid. Although separation by density can be carried out in an optimal manner in this known sorting centrifuge, the substances to be separated definitely require an appropriate primary treatment.
For groups of substances obtained from certain process operations, such as plastic waste contaminated with paper, plastic contaminated with wood, composite materials (plastic/paper) and plastic waste characterized by strongly adhering contaminants which can be removed with water, the currently known methods may include friction separators, turbo driers, primary wash basins and silos all connected in varying sequences with complicated machine arrangements and unsatisfactory results before the separation process proper takes place and with varying, generally unsatisfactory results. For example, friction separators are sometimes mounted upstream of a moist silo which, however, is of no more than little effect because the material is only unsatisfactorily soaked upstream of the friction separator. Even sink-float basins installed upstream as primary washing systems do not reach the intended soaking effect because the residence time of approximately 0.1 to 2 minutes, depending on the length and construction of the basins, is too short. Following subsequent separation by the sink-float method or a hydrocyclone process, the separating liquid has to be additionally removed in a downstream mounted friction or turbo-dryer.